title: HER2 testing: how to reach a high concordance rate between immunohistochemistry and fluorescence in situ hybridization.
abstract: BACKGROUND
  The concordance rate between immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) for human epidermal growth factor receptor-2 (HER2) is still a major clinical concern. We describe a new criteria evaluating HER2 IHC.
  
  
  METHODS
  We expanded the equivocal category to include the American Society of Clinical Oncology and College of American Pathologists equivocal category and cases with 3+ between 30% to 90% of tumor cells and 2+ in ≥1% of tumor cells. Then, we prospectively evaluated 106 cases with FISH.
  
  
  RESULTS
  There were 2 categories that were not required to be tested by FISH based on American Society of Clinical Oncology and College of American Pathologists criteria. The first category, cases with 2+staining between ≥1% and <10%. In this category, there were 15 cases, 2 (13.3%) had HER2 amplification by FISH. The second category, cases with 3+ staining between 30% and 90%. In this category, there were 16 cases, 5 (31.3%) were not amplified and 1 (6.3%) was borderline.
  
  
  CONCLUSIONS
  Expanding the equivocal category could increase the concordance rate between IHC and FISH with minimal additional cost.
authors.affiliation: Department of Pathology, Roswell Park Cancer Institute, Buffalo, NY 14263, USA. thaer.khoury@roswellpark.org
authors.forename: Thaer
authors.initials: T
authors.lastname: Khoury
authors.forename: Swati
authors.initials: S
authors.lastname: Kulkarni
authors.forename: Carl
authors.initials: C
authors.lastname: Morrison
authors.forename: Wiam
authors.initials: W
authors.lastname: Bshara
authors.forename: Yousef
authors.initials: Y
authors.lastname: Zakharia
authors.forename: Stephen
authors.initials: S
authors.lastname: Edge
mesh_terms: D019937:Diagnostic Techniques and Procedures / Q000592:standards; D005188:False Negative Reactions; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence; D008875:Middle Aged; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000032:analysis; D012107:Research Design; D014481:United States; D014486:United States Food and Drug Administration
chemical_list: D018719:Erb-b2 Receptor Tyrosine Kinases; C508053:ERBB2 protein, human